Infrared absorption spectroscopy is growing technology and gaining acceptance in a variety of applications in numerous fields, particularly, the medical and law enforcement fields. Absorption spectroscopy is useful in chemical analysis because of its specificity and its quantitative nature. Also called Fourier Transform infrared spectroscopy, this method of IR spectroscopy measures the amount of infrared light that is transmitted through a sample. Infrared light interacts with the chemical bonds in organic and inorganic materials, and the bonds in such materials will absorb varying intensities of infrared light at varying frequencies. An IR spectrometer registers the infrared light that is absorbed by a material and displays it in a form called an infrared spectrum. The infrared spectral region ranges from a wavelength of about 650 nm, at the red end of the visual spectrum, to a wavelength of about 1 mm, at the microwave region of the spectrum. This wavelength range may be further subdivided into near-infrared (about 650 to about 1400 nm), short infrared (about 1400 to about 3000 nm), mid-infrared (about 3000 to about 8000 nm), long infrared (about 8000 to about 15000 nm), and far infrared (greater than 15000 nm to about 1 mm). Frequently, the near-IR and short-IR ranges depicted herein are referred to generally as “near-IR” with a range of about 650 nm to about 3000 nm. Infrared wavelengths are frequently expressed in units called wavenumbers, expressed as “cm−1” which is the number of waves that fit into a centimeter.
Absorbance bands, or “peaks” that occur at certain wavelengths or wavenumbers represent absorbance of IR light at those wavelengths by molecules as a result of their chemical bonds. As a result, infrared spectroscopy is a technique frequently used to identify molecules and quantify their presence by analysis of their constituent bonds. Each chemical bond in a molecule vibrates at a frequency which is characteristic of that bond. A group of atoms in a molecule (e.g. CH2) may have multiple modes of oscillation caused by the stretching and bending motions of the group as a whole. If an oscillation leads to a change in dipole in the molecule, then it will absorb a photon which has the same frequency. The vibrational frequencies of most molecules correspond to the frequencies of infrared light. Typically, the technique is used to study organic compounds using light radiation from about 4000 to about 400 cm−1, representing the mid-infrared spectral range. A spectrum of all the frequencies of absorption in a sample is recorded. This can be used to gain information about the sample composition in terms of chemical groups present and also its purity (for example a wet sample will show a broad O—H absorption around 3200 cm−1).
When analyzing synthetic and natural materials, near IR absorption spectroscopy has recently shown unprecedented industrial success in multiple applications in grains, forages, baking products, flour, beverages, feeds, pharmaceuticals, dairy products, hydrocarbons and petrochemicals, fine chemicals, radioactive and hazardous materials, and medical imaging and diagnostics. The basic uses of near infrared spectroscopy have been for process control, for quality assessment, for identification of raw materials and process byproducts, and for chemical quantitative analysis of complex mixtures.
To evaluate the presence and quantity of molecules and substances present in a sample, infrared light is passed through the sample. The intensity of the infrared spectra that passes through the sample provide quantitative information (e.g. from the size of the peaks of light measured), and the frequencies of the wavelengths at which absorption takes place in the sample identifies the presence of certain compounds, as no two compounds have the same atomic makeup, thereby producing different frequencies of vibrations between bonds of the atoms making up the material, providing qualitative information about substances in the sample, based on the molecular structures and bonds in the substances. The IR test thus provides a molecular “fingerprint” of the substances present in a tested sample. Generally, for the analysis of clinical specimens, infrared spectra data and reference assays are generated, to serve as calibration samples. Calibration samples permit the identification of specimens that are known, and libraries of calibration samples can also be used to identify unknown substances in the test samples. IR spectroscopy has been growing in its use to detect drugs, such as cocaine in saliva, to detect glucose in diabetes patients, and also to detect biochemical changes in patients, which may be used to detect disease. Near infrared spectroscopy has also been used to test for various compounds in ponds and wetlands.
Additional information concerning infrared spectroscopy related art can be found in the following publications, each of which is fully incorporated herein by reference: T. D. RIDDER,* S. P. HENDEE, and C. D. BROWN, Noninvasive Alcohol Testing Using Diffuse Reflectance Near-Infrared Spectroscopy, APPLIED SPECTROSCOPY, Volume 59, Number 2, 2005; Y. Katsumoto, D. Adachi, H. Sato, and Y. Ozaki, J. Near Infrared Spectrosc. 10, 85 (2002); Y. Katsumoto, D. Adachi, H. Sato, and Y. Ozaki, J. Near Infrared Spectrosc. 10, 85 (2002); and Eli S. Jacoby, Andrew T. Kicman, Paul Laidler and Ray K. Iles, Determination of the Glycoforms of Human Chorionic Gonadotropin β-Core Fragment by Matrix-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry; David A Scott, Diane E. Renaud, Sathya Krishnasamy, Pinar Meric, Nurcan Buduneli, Svetki Cetinkalp, Kan-Zhi Liu, Diabetes-related molecular signatures in infrared spectra of human saliva, Diabetology & Metabolic Syndrome 2010, 2:48; Kerstin M. C. Hans, Susanne Muller, Markus W. Sigrist, IrSens: Sensing cocaine in saliva employing a one-step extraction and MIR spectroscopy, available at http://www.nano-tera.ch/pdf/posters2011/0-0-3-1.png; R. Anthony Shaw and Henry H. Mantsch, Infrared Spectroscopy in Clinical and Diagnostic Analysis, Encyclopedia of Analytical Chemistry; Svetlana Khaustova, Maxim Shkurnikow, Evgeny Tonevitsky, Viacheslav Artyushenko, Alexander Tonevitsky, Noninvasive biochemical monitoring of physiological stress by Fourier Transform infrared saliva spectroscopy, The Royal Society of Chemistry, 2010, Received 16 Jul. 2010, accepted 29 Sep. 2010; Steve Barnett, White Paper: Evaluation of Near-IR Wavelengths for the Detection of Glucose, Acetone, and Ethanol in Saliva.
Currently, the devices and methods available for detection, quantification and analysis of constituents in body fluids or other environmental samples using infrared spectroscopy require drying the samples or other sample manipulation, laboratory apparatus (not portable or field-ready), or measurements from live subjects, subject tissue, etc. For example, U.S. Pat. No. 8,309,931 is directed to rapid methods for diagnosing disease states such as bladder pain syndrome and interstitial cystitis using infrared spectroscopy. However, the method requires collecting a sample, depositing a fraction of the sample on a slide, drying the fraction, and collecting IR spectra to identify the test subject's condition compared to various data models. U.S. Pat. No. 8,406,839 is directed to a handheld device for measuring the concentration of a compound and a value of oxygen saturation in the blood or part of a subject, such as a human or animal. U.S. Pat. No. 5,361,758 is directed to a non-invasive device for measuring the concentration of glucose and other constituents in the blood and tissue of a living human or animal. U.S. Pat. No. 6,236,047 is also directed to non-invasive method of determining blood glucose concentration in a living thing.
What remains lacking in the field of infrared spectroscopic analysis is a device and method for providing clinical precision in liquid samples which can be in remote locations (away from the clinic or laboratory), whereby the device and method operate to isolate focused single or multiple, narrow and wide bandwidths of infrared light for a more accurate identification and quantification of compounds in the samples. The devices and method of the present invention create this ability providing IR spectroscopic sample testing in liquid or solution format to mobile/handheld device platforms.